This invention relates to manhole cover supports for emplacing over and raising the effective grade of an existing manhole cover receiving structure such as the usual cast iron manhole cover frame, and more particularly to manhole cover supports having wales and/or base portions that are box members, especially those cover supports that are arcuate in plan.
For simplicity the term "existing manhole cover receiving structure" is used here to refer to the existing, i.e., fixed in-place frame or other seating receptacle for a removable cover or grating that covers an access hole (i.e., hand hole, tool hole, manhole, catch basin or the like). The term "manhole cover" is used to refer to the removable cover or grating over the access hole. The resulting assembly of a receiving structure and a manhole cover ordinarily is intended to bear vehicular traffic. The term "manhole cover support" or simply "cover support" here means a structure that fits over the existing manhole cover receiving structure, raises its grade, and thereby accommodates a cover or grating at the new elevated grade. The access hole covered is a utility enclosure serving, e.g., an electric, gas, water, sewer or storm drainage system.
Ordinarily the instant cover support finds its use when a roadway such as a street or highway is resurfaced with an added layer of paving material. Typically asphalt concrete is overlaid or repaved to establish a higher grade. It then is advantageous to mount the inventive cover support atop the existing manhole receiving structure. Prior art on manhole cover supports and manhole cover frames can be found in U.S. Pat. Nos. 4,281,944, 4,236,358, 3,968,600, 3,773,428, 4,097,171, 4,302,126, 3,891,337 and 1,987,502. The first four of these are for inventions of the applicant.
Axle loads up to 40,000 pounds must be resisted by many of these cover supports as well as serious impact loads from vehicles and snow plows, a variety of temperature effects, steam leaks, spillage, etc., without permitting a hazardous dislocation of the cover support or its cover. Often it is desirable also to cushion the cover a bit for resisting wear or reducing noise, or to seal the cover and its cover support against a substantial and possibly overloading infiltration of surface water, e.g., storm drainage that otherwise would enter a sanitary sewer system at various manhole locations. Adjustability of the cover support in peripheral dimension and height also is important for accommodating the wide range of specifications to be met.
Installing, adjusting, loading and unloading and otherwise handling manhole cover supports and removing the covers therefrom usually is done with powerful and indelicate tools such as picks, pinch bars, crowbars, tongs, heavy hooks and the like. Deformation of the cover support can occur, particularly about its upper edge which is nearest the road surface. Also, the upper edge usually is the handiest area for applying lifting and other tools. Deformations of the edge never are good, and they can render the opening of the support unfit for service. Hence, overall ruggedness and stiffness against deformation, especially at or near the top rim, and resistance to displacement are major concerns about manhole cover supports.
On the other hand, a relatively light construction of the cover support, in comparison to the ponderous cast iron frame that usually initially supports the manhole cover when the first paving is laid, can be very desirable, provided, however, that an inordinate amount of the ruggedness, stiffness, and resistance to displacement or dislodgement is not sacrificed. Usually a main place for weight reduction is in the lateral keeper for the cover. Another place is in the base of the cover support. Clearly, the economics of manufacture, handling and installation all are generally in favor of lower weight. A relatively thin wall keeper would normally be of steel, rarely no more than about 0.1 inch (12 ga.) thick, usually less.
The instant cover support is an improvement in a cover support with box members, particularly the support of Ser. No. 07/207,185, a parent application referred to above U.S. Pat. No. 4,872,780. That support combined a reasonably low overall weight with a desirable high degree of stiffness; the present improvement makes the support manufacturing, e.g. by cold forming, appreciably easier, and it provides a cover support wherein the metal does not need to be subjected to as much stretching, straining, and attendant thinning and possible deterioration, or the risk of a folding or crimping-in of metal around an inner periphery of the support.
Additionally, this improved cover support can be adapted readily like its parent support to be sealed off against water infiltration and to cushion the cover. It can be made adjustable in its outer perimeter if desired.